Compensated switch



May 23, 1939. L. M. PERSONS 2,159,342

COMPENSATED SWITCH Original Filed May 11. 1956 LAWRENCE M. Person/s,

win/W Patented May 23, 1939 COMPENSATED SWITCH Application May 11, 1930,Serial No. 79,053 Renewed April 3, 1939 3 Claims. (Cl. 200-122) UNITEDSTATES PATENT OFFKIE The present invention comprises a thermallyoperatedcut-oi! operable by applied heat, together with compensating means toovercome the eiiect of extrinsic heat. The mechanism is shown inconnection with an electric switch, although it will be understood to beof broader application.

In general, therefore, it may be said that an object of the invention isto provide a cut-off of this type having means for compensating theefiects of heat other than that directly applied to the instrument.

I It is a further object 01' the invention to provide such a structurehaving the compensating means an integral part thereof.

Referring to the drawing Fig. 1 shows a side view of the switch withelectrical connections shown diagrammatically.

. Fig. 2 is a plan view of the device.

"Fig. 3 is a sectional view thereof on the line 3-3 ofFig. 2.

The switch .comprises a relatively fixed contact In which includes aflexible switch plate element of. generally U-shaped configurationhaving a contact I2 on one of the legs ll thereof, the other leg Hthereof being fixed to'a suitable base. The

connecting member I! of the U-shaped plate is turned up at right anglesto the legs thereof for purposes to be described. A switch blade ithaving a contact". thereon is designed to be brought to the contact l2to establish the circuit. To the switch blade I6 is fixed an insulatingmember I8 and, in turn, to the insulating member I8 is secured one legof a U-shaped bimetal element iii. The other leg of this bimetal elementis attached to a pivot block 20 pivoted at 2| for oscillation.oppositely secured to the pivot block 20 is a second U-shaped bimetalelement 22 having at its opposite end an insulating member 23 beyondwhich is an element 24 fixed to a base 25 by means of a screw 2!operating in a suitable slot 21.

The switch circuit includes a lead 2. connected to the switch blade I 6,and a lead 2! connected to the leg ll of the plate II. This switch maybe interposed in any suitable circuit and, for illustrative purposes, itis here shown as controlling a motor circuit having a motor ll thereinand a power source 3|. The motor may, for example, comprise a furnaceblower to be operated in response to temperature changes in the roomheated by the furnace.

The bimetal 22 constitutes the operating member of the switch. It isheated by a heating coil 32 heated from a power source 13, in circuitwith which is a room thermostat 34 adapted to close when the temperatureof the room drops to a predetermined minimum,

The operation of the device is as follows:

The operating thermal element 22 contracts upon heating, whereas thecompensating thermal element It expands when heated. The two elementsare designed to be equal and opposite in effect, so that the onecontracts the same amount the other expands in response to a giventemperature change. When the room thermostat closes and energizes theheater 82, heat is applied to the bimetal 22 which then contracts. In socontracting, it draws the pivot block 2| and the elements mountedthereon in a counterclockwise direction which, therefore, closes thecontacts" and I2. In this pivotal action of the block 20, the attachingelement 24 is necessarily drawn to the left. This eiiect is permitted bythe slot 21. At the same time the screw" prevents lifting of this end ofthe bimetal 22, so that its entire contraction is transmittedinto thearcuate motion of the pivot block 20. The switch remains closed as longas the heater 32 remains hot. In the illustration given, this will beuntil the furnace motor brings the room up to the desired temperature sothat the thermostat 34 opens. As soon as this occurs, the heater willcool, the bimetal 22 expand, and the switch open.

Necessarily, the bimetal 22 is subject to the eifect of the temperatureof the surrounding air. This temperature might be raised to such a pointthat the bimetal would contract to the same degree produced by theheater 32, or, of course, to any intermediate degree. Any change in theposition of the bimetal 22, unless compensated, alters the spacing ofthe contacts, and time factor of the switch. Any change in spacing ofthe contacts prior to application of the direct heat affects the openingand closing operation of the switch, and may prevent the switch fromopening. The compensating bimetal I! overcomes the eiiect of thesurrounding temperatures and preserves the proper positioning of the twocontacts. It expands, in response to heat changes, the same amount thatthe bimetal 22 contracts. It is, of course, understood that the heaterI2 is so positioned that it produces no substantial effect upon thebimetal I 9. If desired, a baiile plate may be provided between the two.Therefore, if the surrounding atmosphere heats the bimetal 22 andcontracts the same, at the same time, it expands the bimetal IO; sothat, even though the pivot block 20 is shifted under the action of thebimetal 22, the contacts I! and I1 are maintained at the same distanceapart. The

heater 32 normally applies a much more intense heat to the bimetal 22than that applied by the ambient atmosphere. Its eflect, therefore, issuperposed over that of the atmosphere and the resultant action of theswitch is the same as it no atmospheric changes were produced.

As shown, closing 01' the switch is thus effected in response to drop inroom temperature to a predetermined point. When the switch closes, itstarts the motor and thereby causes the furnace to supply more heat intothe room.

The switch plate H is described in my copending application Serial No.80,090, filed May 16, 1936. Its effect is to provide a floating contactthat will break any weld that may occur when the switch is closed. Whenthe contacts seek to part, if there has been a weld, the contact l2 willfollow the contact I 1 during the first part of its motion. A certainamount 01' lost motion is desired in order to give the switch what maybe termed a running start. After this initial running start period,forces are set up in the plate that, in general, may be said to operateabout a pivot at right angles to the pivot 2|. The primary effect of themovement of the co ntact I2 is to lift its leg about the bend where theleg joins the connecting member ii of the U-shaped plate. Clearly, then,if this bend constitutes the pivot of the motion, the lever arm aboutwhich the contact I! moves is much shorter than that about which theswitch arm moves, and at right angles thereto. This produces a wipingaction laterally between the contacts. Also, as this pivotal actionoccurs, the leg I! will bend relative to the connecting member II, asnoted. The joint being flexible, the connecting member I! will turn topreserve its original relation. Said turning is resisted by theconnection with the fixed leg ll. Hence, the result is that as the jointbetween the leg I; and the connecting member tends to unbend, the jointbetween the leg l4 and the connecting member tends to bend further, inthe same degree as the other is unbending. This preserves the originalposition of the contact l2 regardless oi deformation in the plate ll.

Further details of this element are given in the co-pending applicationabove referred to.

What is claimed is:

1. In a device of the kind described, a base, a pivoted element mountedfor oscillation on said base, a first heat responsive means consisting01' a reversely bent bimetallic element secured at one end of thepivoted element and abutting the base at its other end, whereby it actsto pivot said element upon heat changes, a second heat responsive meansin the form of a bimetallic element attached at one end to said pivotedelement, means attaching a contact at the other end or said bimetallicelement, means for applying heat to one of said heat responsive means,whereby to shift the contact, the other of said heat responsive meansacting oppositely to said first in response to heat changes whereby tocompensate for the elect on said contact of ambient temperature changes.

2. In a device of the kind described, a base, a pivoted element mountedfor oscillation on said base, a first bimetallic member attached at oneend to the base and at the other end to the pivoted element whereby itmay oscillate the pivoted element, a second bimetallic member attachedat one end to the pivoted element and adapted to support a switchcontact at its other end, means insulating said switch contact and itscircuit from said bimetallic member, means to apply heat to one of saidbimetallic members, and said members acting oppositely in response toheat changes.

3. In a device of the kind described, a base. a pivoted element mountedfor oscillation on said base, a bimetallic element having a reverse bendtherein, means attaching one end of said element to the base for limitedmovement in a plane parallel to the base but preventing movement awaytherefrom, the other end of the bimetal being attached to the pivotedelement to oscillate the same upon changes in heat conditions, a secondbimetallic element having a reverse bend therein, means securing to oneend of the second bimetal a contact and insulating the same from thebimetal, the other end of the second b etal being secured to the pivotedelement, sai bimetallic elements acting oppositely in response to heatchanges, and means to apply heat to one of them.

LAWRENCE M. PERSONS.

